Bleaching compositions have been used in households for at least fifth to seventy-five years as aids in the bleaching and cleaning of fabrics. The liquid bleaches based upon the hypochlorite chemical species have been used most extensively. These hypochlorite bleaches are inexpensive, highly effective, easy to produce, and stable. The advent of modern synthetic dyes and their inclusion in fabrics has introduced a new dimension in bleaching requirements. Modern automatic laundering machines have also changed bleaching techniques and requirements.
The increasing complexity of modern fabrics and laundering equipment has brought forth a need for other types of bleaching compositions. To satisfy this need and to broaden and extend the utility of bleaches for household use, other bleach systems have been introduced in recent years. Prominent among these are dry, powdered on granular compositions, most usually based upon perborate compositions. These bleaching compositions are generally produced in the dry granular or powdered form. In this form they are relatively stable and do not decompose, or decompose very slowly prior to use. To secure the bleaching effect such dry bleaching compositions are dissolved or dispersed into an aqueous environment at which point they rapidly release the bleaching chemical species.
It has been proposed to use dry bleaching compositions based upon peracid chemical species. The peracid chemical compositions include one or more of the chemical functional grouping: ##STR1## The ##STR2## linkage provides a high oxidizing potential; thus leading to the bleaching ability of such compounds.
The organic diperacid compounds are of particular interest since they form solid materials that are capable of providing the oxidizing linkage.
Although the organic peracids are active oxidizing agents and useful in fabric bleaching, they suffer from a number of defects which can seriously interfere with their commercial use. One serious shortcoming is their tendency to undergo exothermal decomposition. Another is their inherently poor shelf stability. And another defect is their odor, which in general is perceived as acrid and obnoxious.
Much effort has been expended to reduce or eliminate the defects of the organic peracid compounds to adapt them to the commercial and, especially, the household market. It has been determined that the tendency to decompose can be eliminated, or greatly reduced by mixing the organic peracids with diluents, or exotherm control agents. U.S. Pat. No. 3,770,816 issued Nov. 6, 1973 to Nielsen, and U.S. Pat. No. 3,494,787 issued Feb. 10, 1970 to Lund et al, discuss the use of hydrated alkali metal or alkaline earth metal salts as a means to control the exothermal deterioration of peracids. U.S. Pat. No. 4,100,095 issued July 11, 1978 to Hutchins et al. suggests the use of acids that liberate water upon heating, e.g., boric acid, as exotherm control agents. This patent however also indicates that the hydrated salts, are to be avoided as exotherm control agents. The patent notes that hydrated salts develop sufficient vapor pressure in the presence of diperacids to cause an increase in the loss of oxygen.
The moisture level in dry peracid products can also affect their shelf-life. Since water facilitates release of active oxygen, careful control of its presence must be maintained in the dry bleach formulation, otherwise premature deterioration of the peracid takes place.
Although the addition of exotherm control agents may effectively alleviate the decomposition problem, a new problem is introduced thereby. As the agents are added to the peracids, the amount of active oxygen released for bleaching is often reduced. Active oxygen is defined to mean the total equivalents of oxidizing moities in the peracid compound. (See S. N. Lewis, "Oxidation", Vol. 1, Chap. 5, R. Augustine, Editor., Marcel Dekker, N.Y., 1969; pp. 213-258) Actual active oxygen release is often less than the stoichiometric or theoretical yield calculated from the active oxygen content of the peracid.
In any event, the addition of exotherm control agents reduces the level of the active oxygen yielded from unstabilized peracids and therefore reduces the efficiency of the peracid composition. This increases the per unit cost, or effectiveness of the stabilized peracid composition. Thus the solution of one problem, raises another problem.
Other problems associated with peracid bleaches stems from their inherent bleaching ability. In this regard, fluorescent whitening agents (FWA's) are desirable components for inclusion in bleaching formulations. They counteract the yellowing of synthetic and cotton fibers. They function by settling out on fabrics during the washing and/or bleaching process, where they absorb ultraviolet light, and then emit visible light, generally, in the blue wavelength ranges. The resulting light emission produces a brightening and whitening effect, thus counteracting any yellowing or dulling of the bleached fabrics.
Unfortunately, however, the FWA's are rather easily oxidized. In the presence of oxidizing agents such as the peracids, they are subject to deterioration and their desired whitening effect is lost. Thus steps must be taken to protect the FWA's from premature oxidation.
The acrid, unpleasant nature of odors released by peracids also presents a continuing problem in securing market acceptance. Some solution to this problem is also necessary.
The present invention solves all of the above and other problems associated with diperacid based bleaching products.